1. Field of the Invention
The present invention relates to a control system and a control method for a link structure which is constructed by connecting a plurality of rigid bodies, and a robot apparatus, and particularly, to a control system, a control method, and a robot apparatus which sense an unknown environment and obtain a proper external force from surrounding environments which vary every moment, thereby properly adjusting the generating forces of actuators so that a desired task may be achieved.
More specifically, the present invention relates to a control system, a control method, and a robot apparatus which perform not only the precision of positions or postures but dexterous operation of forces, and realize services accompanied by interaction with persons or objects, and particularly, to a control system, a control method, and a robot apparatus which exactly solve a mechanical model while external forces having contact parts as points of action are properly used, thereby determining the generating force target value of each joint actuator, and which compensate a force which is difficult to model in each joint, thereby realizing favorable tactile force interaction in which points of actions are not limited.
2. Description of the Related Art
With the rapid arrival of an aging society, it is expected that the ratio of elderly people and productive-age population which supports the elderly people will be 1 person:2.4 persons in 2015, and 1 person:2.1 persons in 2025 from 1 person:3.3 persons at the present time (2005). As such, it is imperative to make the elderly people whose ratio occupied in the composition of population increases rapidly live as healthily and actively as possible without requiring nursing care, and to make a society in which relapse can be prevented as much as possible even if the elderly people require nursing care, and they can lead independent lives.
With the arrival of such an aging society, the need for mechatronics instruments aiming at assistance in elderly people's minds and bodies is increasing in elderly-people nursing care facilities or at homes which have elderly people. Further, the need for mental assistance in which robots are effectively incorporated in occupational therapy as well as physical assistance called power assistance of walking aids or upper limbs exists.
In the above field, the mechatronics instruments should execute a task while making physical contact with people or complicated actual environments flexibly and safely. That is, unlike the fact that existing industrial robots performed fixed motions under a known environment, the above mechatronics instruments should sense an unknown environment and obtain a proper external force from surrounding environments which vary every moment, thereby properly adjusting the generating forces of actuators so that a desired task may be achieved.
As such an environment-adaptive robot control method, for example, a control method of measuring a peripheral environment shape using a stereoscopic view using a plurality of cameras, or a laser range finder, and correcting the position and posture of a robot so as to suit the above shape is tried in the related art (for example, refer to “A Modular Architecture for Humanoid Robot Navigation” (Proceedings of 2005 5th IEEERAS International Conference on Humanoid Robots, pp. 26-31), and “Vision-based 2.5D terrain modeling for humanoid locomotion” (In Int. Conf. on Robotics and Automation (ICRA), Taipei, Taiwan, 2003)). However, this control method has a problem in that updating rate is low because not only the precision of the cameras is required, but the amount of operation when the peripheral environment shape is reproduced on the basis of measurement results increases. Further, since this control method is based on positional control, it is considered that it is difficult to reactively adapt to an environment.
The positional control is commonly called “hard control” because its basic purpose is to hold a position, and is not suitable for responding to an external force flexibly or for precisely performing the control of velocity or acceleration. For example, robot apparatuses which execute a task while performing physical interaction with various outsides originally have low compatibility with the positional control.
In contrast, it is considered that force control is ideally driven by a force control system although a control law or a system construction becomes complicated. For example, a method arranging a force sensor in an end effector or a leg part, and manipulating a surrounding object while measuring an applied force from an environment, or adapting a robot to an irregular ground is also suggested (for example, refer to “Force Feedback Sensor” (Journal of Robotics Society of Japan, Vol. 6, No. 9, pp. 759-765, 1991), and “Development and Application of a Robot Surface Multiple-valued Contact Sensor” (Lecture Draft Collections of Robotics and Mechatronics Lecture Meeting 98 by Japan Society of Mechanical Engineers, 1CI1-2, 1998)). However, it is technically difficult to arrange force sensors so that the sensors can detect forces acting on a robot body without omission, and as a result, it is considered that parts where contact with an environment is not permitted may be generated. In other words, in order to exactly solve a mechanical model to realize tactile force interaction, the point of action of an external force is limited.
Although investigations in which contact sensors are arranged in a distributed manner on a whole body in order to acquire a contact state with an environment are also mentioned (for example, “Development and Application of a Robot Surface Multiple-valued Contact Sensor” (Lecture Draft Collections of Robotics and Mechatronics Lecture Meeting 98 by Japan Society of Mechanical Engineers, 1CI1-2, 1998), “Development and Application of Flexible Tactile Sensor for Robots Using Conductive Gel” (Draft Collections of 16th Academic Lecture Meeting of Robotics Society of Japan, 873-874, 1998), and
“Whole-Body-Coated Tactile Sensor Using Conductive Fabric” (Journal of Robotics Society of Japan. Vol. 16, No. 1, pp. 80-86, 1998)), sufficient consideration is not performed from the viewpoint of mechanics or control, such as whether it is desirable what degree of force should be imposed on a contact point in order to achieve a task. For this reason, even if the contact state with an environment can be detected, it cannot be said that the capability for achieving a target task under this contact state has been achieved.
Although a torque calculation method of exactly solving a mechanical model to determine the joint torque for generating a specified force in a predetermined part is also suggested (for example, refer to “A prioritized multi-objective dynamic controller for robots in human environments” (In Proceeding of the IEEE/RSJ International Conference on Humanoid Robots, 2004)), an attribute (disturbances), which is difficult to model, resulting from gear friction, etc. is included within a joint. Thus, there is a problem in that, unless this main attribute is properly handled, an error may be caused, and vibration may be excited.
A further example of the related art includes JP-A-5-305583.